Modern aircraft often use a variety of high lift leading edge and trailing edge devices to improve high angle of attack performance during various phases of flight, for example, takeoff and landing. One such device is a leading edge Krueger assembly 10, shown schematically in an extended position in FIG. 1. When the Krueger assembly 10 is in the extended position, it can improve the airflow characteristics over a wing 40 at high angles of attack, allowing the wing 40 to operate at higher angles of attack without stalling.
The Krueger assembly 10 includes a first surface 11, a second surface 12, six links that connect the Krueger assembly 10 to the wing 40, and an actuator 30. The actuator 30 includes a torque tube 31 with a lever 32. The lever 32 is pivotally connected to a first link 14 at point Q. The first link 14 is also pivotally connected to a second link 16 at point S. The second link 16 is pivotally connected to the wing 40 at point R and pivotally connected to a third link 18 at point T. The third link 18 is pivotally connected to the first surface 11 at point U.
The first surface 11 is pivotally connected to the wing 40 at point O. As the actuator 30 rotates the torque tube 31, the lever 32 moves the first link 14, which in turn moves the second link 16 and the third link 18. The third link 18 causes the first surface 11 to pivot about point O.
The second surface 12 is pivotally connected to the first surface 11 at point P. Three additional links coordinate the movement of the second surface 12 relative to the first surface 11. In particular, a fourth link 20 is pivotally connected to the wing 40 at point V and pivotally connected to a fifth link 22 at point W. The fifth link 22 is pivotally connected to the first surface 11 at point X and pivotally connected to a sixth link 24 at point Y. The sixth link 24 is pivotally connected to the second surface 12 at point Z. As the actuator 30 moves the first surface 11, the second surface 12 is moved in a coordinated manner relative to the first surface 11 by the fourth link 20, the fifth link 22, and the sixth link 24.
The Krueger assembly 10 can be retracted to form a lower portion of the wing 40. In FIG. 1, the first and second surfaces 11, 12 are shown in the retracted position by dotted lines. The retracted position is suitable for cruise and other low angle of attack operations. In order to move the Krueger assembly 10 from the retracted to the extended position, the actuator 30 rotates the torque tube 31 in the direction of the arrow R1.
During extension, the second surface 12 rotates relative to the first surface 11 about point P as both surfaces move to the extended position. As the two surfaces transition through an intermediate position where the first surface 11 is approximately perpendicular to a chord line 42 of the wing 40, the second surface 12 rotates relative to the first surface 11 so that it extends below the first surface 11, as shown by dashed lines in FIG. 1. This arrangement presents a large surface area to the relative wind (arrow W) during extension. Accordingly, the drag created by the first and second surfaces 11, 12 as the Krueger assembly 10 transitions through this intermediate position can be greater than the drag of the first and second surfaces 11, 12 in the extended or retracted positions.
Although the Krueger assembly 10 only has one extended position, the actuator 30 can also be connected to other devices (not shown) that have multiple extended positions. Accordingly, once the Krueger assembly 10 is moved from the retracted position to the extended position, the actuator 30 can rotate an additional amount in the direction of arrow R1 to move the other devices to additional extended positions. As the actuator 30 rotates by this additional amount, the torque tube 31 moves the lever 32, which moves the first link 14 as shown by ghosted lines, but leaves the first and second surfaces 11, 12 in generally the same extended position. A drawback with the system discussed above and shown in FIG. 1 is that it is complex (using six links with ten pivot points) and therefore costly to manufacture and maintain.